1. Field of the Invention
The present invention relates to a graft-modified copolymer and, more specifically, it relates to a graft-modified copolymer derived from the graft modification of low crystalline or amorphous ethylene-alpha-olefin copolymer having specified properties with a styrene-type hydrocarbon. This graft-modified copolymer is suitable for use as a compounding agent for improving the impact resistance of styrene-type polymers without decreasing the surface hardness, weathering resistance, and molding properties thereof.
2. Description of the Prior Art
Heretofore, various methods for obtaining polystyrene and other styrene-type polymers having improved impact resistance by compounding rubber-like elastomer into general-purpose (GP) polystyrene and other similar resins having high stiffness are known. It has also been proposed that a rubber-like elastomer graft-modified with a styrene-type hydrocarbon is compounded to improve the compatibility between a polystyrene phase and a rubber phase. For example, high-impact (HI) polystyrenes, ABS resins and other styrene-type resins having appropriate stiffness and impact resistance are widely utilized in various application fields after treating with the above-mentioned modification methods. However, the resultant resin compositions have a disadvantage that the weathering properties are poor because polybutadiene and other diene type rubbers are used as a rubber-like polymer compounding agent for providing impact resistance to styrene-type polymers in the conventional methods. For example, these resin compositions are limitedly utilized for outdoor use because they are subjected to extreme ultraviolet degradation and ozone degradation. This is a largest disadvantage of HI polystyrenes, ABS resins and other styrene-type resins.
Recently, various attempts to improve impact resistance of styrene-type polymer compositions without decreasing the weathering resistance, surface hardness, and molding properties have been made. For example, various methods in which rubber-like elastomers graft-modified with styrene-type hydrocarbons and having no carbon-carbon double bond in the polymer molecule are used as a compounding agent in lieu of the above-mentioned diene-type rubber-like elastomers graft-modified with styrene-type hydrocarbons have been proposed. Examples of such compounding agents are acrylic acid ester type rubbers, ethylene-vinyl acetate copolymers, and chlorinated polyethylenes. The weathering properties of the styrene-type resin compositions containing the above-mentioned compounded rubber-like elastomers are improved. However, these styrene-type resin compositions have the disadvantages of poor thermal properties such as poor low-temperature characteristics and poor heat aging resistance. Therefore, the application fields thereof are limited.
Furthermore, it has been proposed that styrene is polymerized in the presence of the above-mentioned rubber-like elastomers to disperse the rubber-like elastomers in styrene-type polymers. According to this method, two different reactions of a graft reaction of styrene onto the rubber-like elastomer and a homopolymerization of styrene simultaneously proceed to produce a styrene-type polymer composition containing the above-mentioned rubber-like elastomer compounded therewith. However, it is difficult to obtain a resin composition having excellent impact strength and excellent weathering resistance and molding properties in this method since it is difficult to control both reactions for the optimum physical properties of the resultant resin composition become.